WHAT IS a CV Axle?
CV (constant-velocity) axles, (also known as half-shafts), are used in front-wheel drive vehicles to transfer the engine’s power from the transaxle to the two drive wheels. Some late model vehicles with independent rear suspension and some four-wheel and all-wheel drive vehicles also use CV axles.
A CV axle has two CV joints (an inner joint and an outer joint). These joints allow the axle to transfer the engine's power to the drive wheels at a constant speed while accommodating for the different travel conditions, including the up and down motion of the suspension and cornering. Without constant-velocity joints, the axles would bind or break whenever the vehicle hit a bump in the road or turned a corner.
CV joints are packed with grease for lubrication. To keep the grease in the joint and moisture, dirt and roadway grime out, the joint is covered with a rubber boot called a CV boot. CV boots are made of a durable rubber that can withstand extreme weather and travel conditions. Good quality CV boots can easily last 100,000 miles or more. But, because they are constantly exposed to the elements, a CV joint boot can be damaged at any time. For this reason, it is a good idea to routinely inspect your CV boots for damage. If your vehicle has more than 125,000 miles - it is a good idea to check the CV joints more often.
Actually, CV axles rarely fail - it's the CV joint(s) that fail and they typically only fail because of a damaged or torn CV boot. When a CV boot fails due to age and wear, or is damaged by roadway debris, the grease that keeps the joint lubricated quickly leaks out of the joint and dirt, roadway grime and moisture enters the joint. When this occurs, the CV joint will soon fail.
Of the two joints, the outer CV joint almost always fails first because it does more work than the inner joint so it wears out sooner. The outer joint is also much more likely to be damaged from roadway debris because of its location. For these reason, if you suspect CV-joint failure, odds are it is the outer joint that has failed. (See above image)
NOTE: While a damaged or torn CV boot is almost always to blame for a failed CV joint, like any part, CV joints can wear out over time. As the joint ages and wears, tight tolerances give way to added space opening up between the moving parts of the joint. As space between the parts increases the parts begin to bang against each other and after awhile they break.
Symptoms of a Bad or Failing CV Joint
A bad or failing CV joint will oftentimes make a clicking, popping or grinding noise, especially when turning. At low speed, a bad CV joint may make a steady knocking sound every couple of seconds or so. A bad CV joint can also cause a vibration that is felt in the steering wheel and floorboard of the vehicle - this may happen only at certain speeds.
INSPECTING a CV Axle and Checking/Testing a CV Axle
A routine inspection of the CV axles and CV boots and checking/testing a CV axle you suspect of being bad are two different processes. Below is an explanation.
Routine CV Axle Inspection
Inspecting a CV axle involves a visual check of the CV boots. In most instances, all you will need is a flashlight.
Follow these Steps...
Checking/Testing a CV Axle You Suspect of Being Bad
Checking and testing a CV axle you suspect of being bad or beginning to fail involves a visual inspection, a movement test and a drive test.
Follow these Steps...